1. Field of Invention
This invention relates to piano key mechanisms, and more specifically to improvements in measuring the performance characteristics of key mechanisms of a piano or keyboard.
2. Description of the Prior Art
A. Measuring “Static” Key Forces
There is a longstanding practice of measuring “static” values of Down Weight, Up Weight, and (indirectly) Balance Weight and Friction, by applying “gram weights” to the keys of the piano action. New methods and apparatus were disclosed in U.S. Pat. No. 8,049,090, by the present author, which eliminated the need for the old “gram weight” techniques, producing more scientific and repeatable results. These new methods involved reaction forces at the key being measured continuously during constant-speed downstrokes and upstrokes, resulting in continuous force data for the stroke. In addition, averages of these forces were described, being declared as “replacements” for the old parameters of Down Weight, Up Weight, Balance Weight and Friction Weight.
A clever mechanism was built and used on a piano action in the 1920's. It was able to depress a piano key gradually, due to a manual “sliding” adjustment of a horizontal lever (containing a “pen” that drug across nearby graph paper). The other end of the lever—opposite a pivot—rested on the piano key. When the sliding changed the moment arm of the lever sufficiently to further displace the key, the entire lever (with pen) would rotate, dragging the pen across the paper. The force was therefore not actually measured, but rather known by the moment induced by the sliding member. The force could therefore change only very gradually with key displacement, allowing for only very primitive information with regards to “dynamic” events such as the escapement. The displacement was not controlled in any way, with the rotation of the member being dependent upon the current resistance offered at its contacting point with the key.
B. Key Leveling
Included in the process of regulating a piano is the act of “leveling” the keys, in both their “at rest” and “depressed” states. This leveling process generally involves measuring (or checking) the key locations (vertically) first, followed by adding or removing various punchings or spacers to/from the Balance Rail and/or the Front Rail.
“Reference bar” methods of “at rest” Key Leveling have been used for many decades in the industry. They consist of laying a “reference edge” of a “reference bar” against two or more “point” datums, the datums being approximately in the designated Vertical AP Plane for the given-colored keys being measured. This method seems to be more often used for white keys, and less often for black keys. Whether the “reference edge” is linear or not, it establishes the “zero line”, against which the key tops are compared. With these “reference bar” methods, the “reference edge” is usually considered to be the desired location for the various key tops. The vertical distance from the “at rest” AP of each same-colored key to the “reference edge” of the bar is noted and/or measured. For each key, this distance tells the technician how much “shimming” needs to be added or removed at the Balance Rail of that key.
In the past 30 years, at least two “passive displacement” gauges have been offered on the market, designed to measure both the “at rest” and “depressed” key locations, relative to a “global” reference plane. Various types of small blocks and gauges have also been used throughout the years to determine the “depressed position” of the key. In addition, the present author disclosed methods and means—in U.S. Pat. No. 8,049,090—for “active” determination of the Key Dip, using a kinetic, well-controlled, force-sensing manipulator. This allowed the key's exact location and resisting force (due assuredly to compression of the front punching) to be quickly and simultaneously created and measured, respectively—with no reliance upon the technician/operator.
C. Measuring Key Action Inertia and “Sluggishness”
A significant problem in the area of piano manufacture and piano action repair is that of the true “feel” of the piano keys not being measurable or quantifiable. There is no way in the prior art of kinetically determining the inertial properties of a key mechanism, or even an individual key action component. And certainly there is no non-invasive way of measuring key action inertia. The limited methods that have been utilized in obtaining numbers related to inertia normally involve significant disassembly of the key mechanism and simple stationary weighing of components. There is no way in the prior art of measuring inertial forces on any one of a multitude of different key actions, resulting from some known acceleration or series of accelerations. Nor has a way been established of turning such “inertial force” data into intrinsic inertial properties of the key mechanism. There is also no way in the prior art of directly measuring and quantifying the “sluggishness” of a key action. The only existing indicator that has sometimes been used to describe how readily a key will rise from a depressed position is the Up Weight. It is, however, a very indirect indicator of this ability, having very limited value in this regard.
What is therefore needed is a means of accurately quantifying and measuring the true resistance to accelerated motion (i.e., the total inertia)—as felt at the key during an accelerated downstroke—of any key action. This “resistance to accelerated motion” must be due solely to mass and its distribution in the mechanism, and not to any “down force” effects (such as friction, springs, gravity or magnets). The ability to measure inertia would allow the key actions of a piano to be judged objectively and accurately as to their true “dynamic resistance” during the act of playing a piano. Also needed is a way of directly and quantitatively measuring the ability of a key to return to its rest position, from some depressed position.
The inertia determination might also be done on the “component” level. That is, by focusing on individual components of the key action and accelerating/measuring them in some fashion to obtain their “local inertia” about a convenient axis. Once a “local inertia” value is obtained, knowing certain geometric or moment ratios in the action might then allow one to calculate that component's equivalent inertia at the key.